Limit to number of parents an object can have?
A certain object can only have 1 parent in Blender. You don't need to worry about not being able to control the object the way you want to, because you can also control the parent objects, and so on and so forth. In my example I parented the hooks of the eyes, in which case if both are moved together at the same time will move the entire eye, to a single empty that will move the eye. I did this for both, and parented those empties to a third empty that rotated them around the sphere. Then I parented that empty to the sphere itself so that when I move the sphere, everything moves. I thus solved my own problem.